Cell for electrolysis with molten salt electrolyte



March 1968 E. MEIER ETAL CELL FOR ELECTROLYSIS WITH MOLTEN SALTELECTROLYTE Filed Nov. 7, 1963 SUPPLY FEED DUCT FOR METAL HALIDE 6 W mwe EE .l. M m P E OF PD G RR 0 E F um X M NA E0 E6 NH LZ F FF E i l w Nn A CATHODE EVAPORATING cmmasn ORIFICE m ANODE VESSEL/ w w Edw/h Meierand Er/ch 5chwe/Zer INVENTOR ATTORNEY United States Patent ABSTRACT OFTHE DISCLOSURE An electrolytic cell is provided for the manufacture ofmetals of the 4th, 5th and 6th sub-groups-of the Periodic Table from thehalide of the metal in a molten salt electrolyte. The cell has a hollowcylindrical anode and a rod-shaped cathode. The cathode is positionedwithin and coaxially aligned with the anode. The anode is characteriz edby havinga plurality of annularly-arranged holes which extenddownwardfrom the inner wall of the anode to the outer wall of the anode. Thecell has a downward-opening annular chamber positioned'about the outerwall of the anode. In operation the cell is filled with a molten saltelectrolyte to a level-at which the surface of the electrolyte isslightly above the holes in the anode and in commu nica t ion with theopening of. theannular r. A. PQ ZQ me a ha id i e in the annular chamberfrom where it is introduced into the elec-" trolyte. The holes in theanode assist the circulation of the electrolyte and facilitate theremoval ofthehalide gases from the electrolyte in the cell.

Several electrolysis cells are. known for the production of heavymetals, by electrolysis by the. continuousaddition of a metal halide toamoltensalt electrolyte. In some cases it has been proposed to supplythernetal halide bya special supply feed directly to the cathode, or tointroduce it into the melt bath through a hollow cathode. There are alsoknown cells. with a cylindrical anode and a rod-shaped cathode arrangedcoaxially thereto. r

\ One of the main difficulties in the manufacture of heavy metals byelectrolytic means is to discover conditions under which metal separatesin as pure a state as possible.

I Special 'diificulties halide is added in vaporous state. Thecomposition ofthe bath, the electrolysis temperature, the-material ofcathode, anode, vessel and diaphragm .and the arrangement of theindividual elements of the cell'influence the electrolysis and,consequently, the quality and quantity of the metal separated. Thearrangement-and constitution 'ofthe cell present invention conis ofparticular importance. The cerns this problem and provides possible tomanufacture especially It-has been found puremetals sub-group of thePeriodic Table the corresponding metal halide if the cell has thefollowacell which makes it pure; metal. 7 of the'4th,- 5th and 6t ing features:

(l) The cell has no supply duct for the-metal halide vapour intothemelt, but only an arrangement whereby the metal halide is supplied tothe surface of the melt".

Thus, the metal halide is not introduced but ifiows on to the surfacewhere it is absorbed bytthe molten salt bath on account of convection.The elimination of a duct submerged into the melt also eliminates the.difiiculty of having to introduce the metal halide under pressure. Induct also prevents any addition, the elimination of the additionalcontamination of'the-melt.

(2) An essential feature of the invention; is that the condensingchamber for the metal halide, i.e., the place are encoun ter ed, whenthe metal 1 may be produced from where the halide is absorbed by themolten bath, is outside the zone of the electrolysis. According to theinvention, it is arranged concentrically around electrolytic zone. Thisarrangement avoids losses of metal halide, such as occur during thecondensation of the halide vapour in the electrolytic zone by dischargewith the anode gas. Condensing chamber and electrolytic zone correspondto the principle of communicating vessels so that the level of the bathis the same in both parts of the cell.

(3) The cylindrically shaped anode contains in its upper portion,slightly below the level of the melt, several orifices in annulararrangement. These orifices produce a continuous circultion 0f the bath.In the inner part of the anode cylinder, the bath rises, flows throughthe orifices and down along the-outside of the anode. In the inner partof the cylindrical anode, the halide is produced and the formed gasbubbles support the upward movement of the circulation in this zone.

(4) A special advantage of the arrangement of the invention is that nodiaphragm is necessary. The supply of the metal halide vapour outsidethe electrolytic zone and the described circulation of the molten bathresult in optinum conditions for the electrolysis so that no diaphragmis necessary.

The present invention relates to a cell for the electrolysis of halidesof metals of the 4th, 5th and 6th subgroups of the Periodic Table in amolten salt electrolyte, equipped with a feed duct for the vaporousmetal halide and with a rod-shaped cathode, arranged coaxially within acylindrical anode, characterized in that the condensing chamber for themetal halide is located outside the electrolytic zone, that the anodehas preferably cylindrical holes in annular arrangement, slightly belowthe horizontal plane forming the upper defining line of the effectivepartof the rod cathode, and that there is arranged on the outside of theanode cylinder a downwardly open bath is at the same time the upperlimit of the active.

part of the cathode rod. Below this limit there are the openings in theanode and, above, there is the non-irnmersed part of the annularchannel, i.e., the socalled condensing chamber.

-. is shown at 6, a delivery duct at 7, and the outlet of thehalogengases formed at the anode at 8. Reference numeral 9 indicates ahinged cover. The vaporous metal halide enters at 10 and passes through11 into the annular channel 12.'The bath 13 circulates as indicated bythe arrows. -14 is'an orifice in the cylindrical anode. These v orifices14- are preferably of cylindrical shape, the longitudinal axisof thecylinder sloping downwardly toward the outside. This arrangementprevents the anode gas from being carried along into the condensingchamber. The supply feed duct 11 for the metal halide vapour terminatesconveniently in the top of the annular channel 12.

Preferably a' hollow cathode is used, with a watercooled holder, andmade of nickel. The cylindrical anode,

as well as the vessel, are made of graphite. The top of r the cell isclosed so that access of foreign gases, such as air, is prevented.

above which horizontal plane The melts consist of mixtures of alkalineand alkaline earth halides, such as KCl, NaCl, KF, NaF, CaClor CaFPreferably mixtures are used which produce, after addition of the metalhalide, stable double salts of the metal to be separated with thefluorides present in the bath.

The cell is suitable for producing titanium, zirconium, vanadium,chromium, molybdenum, tungsten, and especially tantalum and niobium. Themetal halides supplied as vapours are especially metal chlorides, suchas TiCl VCl VOCl NbCl TaCl and WCI and WOCL EXAMPLE 1 In an electrolyticcell according to FIG. 2, about 40 kg. of a salt mixture, consisting of40% sodium chloride, potassium chloride and 30% potassium fluoride, aremolten at about 800 C. Into this melt, about 7 kg. tantalumpentachloride are added as vapour by convection through conduit 11 andannular channel 12. Electrolysis is effected at a bath temperature of800 C. to 900 C. with 1500 amps. In order to maintain the concentrationof tantalum chloride in the melt, 3.6 kg. TaCl are introduced in thecourse of one hour. After one hour, the separated metal is removed fromthe cell and further electrolysis is carried out with a second cathode.1710 grams of tantalum are separated during this time. The yieldrelatedto TaCl is 95% and the mean current yield is 83%. The metal produced hasa uniform, metallic appearance and consists of dendrites of 100 to 500microns. An analysis shows the following impurities:

Percent, below Carbon 0.02 Oxygen 0.02 Hydrogen 0.002 Nitrogen 0.005Silicon 0.001 Tungsten 0.003 Molybdenum 0.001 Niobium 0.005 Chromium0.005 Nickel 0.01 Iron 0.005 Titanium 0.001

EXAMPLE 2 A cell as shown in FIG. 2 is used. 2.5 kg. of titaniumtetrachloride are added as vapour through annular channel 12 andabsorbed in kg. of a basic melt consisting of percent by weight ofsodium chloride, 40 percent by weight of potassium chloride and 20percent by weight of potassium fluoride; electrolysis is carried out for1 hour at 1000 amps. and at a bath temperature of 800 C. A further 2.5kg. of titanium tetrachloride are added as vapour during electrolysis.The Separated metal on the cathode is cooled in an atmosphere of argon;after washing, the weight of the metal is 327 grams which corresponds toa current yield of 72.6% and a metal yield of 89%. An analysis shows thefollowing values:

Percent, below Carbon 0.02 Oxygen c 0.02 Hydrogen 0.005 Silicon 0.001Molybdenum 0.001 Chromium 0.01 Nickel 0.03 Iron 0.02 Tungsten 0.003

EXAMPLE 3 In each case a cell as shown in FIG. 2 is used.

(a) 6 kg. of tungsten hexachloride are added as vapour into a basic meltof the same composition as described in Example 2 and electrolyzed asdescribed in Example 2.

- 4 I Y The washed metal Weighs 784 grams. The current yield is 68.4%,the metal yield 83%. a

(b) 4 kg. of tungsten oxychloride are added as vapour into the abovemelt and subjected to electrolysis at 1000 amps for 1 hour to yield 724grams of metal. The current yield is 63%, the metal yield 85%.

An analysis shows the following values:

' Percent, below Carbon 0.03 Oxygen 0.03 Hydrogen 0.005 Silicon -2 0.001Molybdenum 0.001 Chromium 0.01 Nickel 0.03 Iron 0.02 Titanium 0.001

, EXAMPLE 4 A'cell as shown in FIG. 2 is used. A total of 3 kg. ofniobium pentachloride is added as vapour through annular channel 12 intoa basic melt of 17.1 kg. of sodium chloride, 9.8 kg. of potassiumchloride and 13.0 kg. of potassium fluoride. The bath temperature is 900C. Electrolysis is carried out for 1 hour with 1200 amps. The weight ofthe metal separated during this time amounts, after washing, to 310grams, which corresponds to a current yield of 37.2%. After analysingthe niobium remaining in the melt, a material yield of 89.5% was found.

An analysis shows the following values:

- Percent, below Carbon 0.03 Oxygen 0.03 Hydrogen 0.005 Silicon 0.001Tungsten 0.003 Molybdenum 0.001 Tantalum 0.01 Chromium 0.01 Nickel 0.03Iron 0.02 Titanium 0.001

What is claimed is:

1. Cell for the electrolysis of halides of metal of the 4th, 5th and 6thsub-groups of the Periodic System, in a molten salt electrolyte, havinga supply feed for the vaporous metal halide and a rod-shaped cathode,arranged coaxially within a cylindrical anode, characterized in that thecondensing chamber for the metal halides is outside the electrolyticzone; that the anode has cylindrical holes in annular arrangementslightly below the horizontal plane forming the upper defining line ofthe eifective part of the rod cathode the remainder of said anode beingnon-fora-minous, said holes having a cylindrical shape and theirlongitudinal axis sloping downwardly and outwardly, and that adownwardly open annular channel is arranged on the outside of thecylindrical anode, extending from said holes upwardly to above thehorizontal plane forming the upper definition of the effective part ofthe rod cathode, above which horizontal plane there terminates at leastone supply duct for the vaporous metal halide in this annular channel.

2. A cell as claimed in claim 1, characterized in that the supply ductfor the metal halide terminates in the top of the annular channel.

3. An electrolytic cell for the manufacture of the metals of the 4th,5th and 6th sub-groups of the Periodic Chart from a-halide of saidmetals using a molten salt electrolyte, said electrolytic cellcomprising in combination 1' downwardextending apertures from the innerwall to the outer wall arranged annularly about said anode at a positionwhich is only slightly below the surface of the electrolyte when theanode is emersed to said predetermined level, the remainder of saidanode being non-foraminous said annular chamber being positioned aboutthe outer wall of the anode so that it is in communication with thesurface of the electrolyte when the anode is emersed to thepredetermined level, and said supply duct being in communication withthe annular chamber and adapted to feed said metal halide, in vaporizedform, to the annular chamber.

References Cited UNITED STATES PATENTS 2,898,276 8/1959 Snow 204246 X2,908,619 10/ 1959 Barnett 204-246 X 3,079,324 2/1963 Allen et a1.204-246 HOWARD S. WILLIAMS, Primary Examiner. JOHN H. MACK, Examiner.

l D. R. VALENTINE, Assistant Examiner.

